Apparatus for hydrocarbon ignition and monitoring



Oct. 11, 1966 wALBRlDGE 3,277,949

APPARATUS FOR HYDROCARBON IGNITION AND MONITORING Filed April 1, 1965 2 Sheets-Sheet 1 La v i 2 j V 38/ 3 i 35b 32 22 r I 35 r; ITHERMOSTATI I80 U I8 I 5 l6 5/30 |2 A w v I 655 Ki/\L t v u u V V6? V INVENTOR. LYMAN H. WALBRIDGE Bar/ 2W7, N am ATTORNEYS Oct. 11, 1966 1.. H. WALBRIDGE 3,

APPARATUS FOR HYDROCARBON IGNITION AND MONITORING Filed April 1, 1965 2 Sheets-Sheet 2 FIG. 5

ATTORNEYS United States Patent 3,277,949 APPARATUS FOR HYDROCARBON IGNITION AND MONITORING Lyman H. Walbridge, Ashland, Mass, assignor to Fenwal Incorporated, Ashland, Mass, a corporation of Massachusetts Filed Apr. 1, 1965, Ser. No. 446,782 24 Claims. (Cl. 158-125) This application is a continuation-impart of my copending application Ser. No. 378,840, filed June 29, 1964, and now abandoned.

My invention relates to a method and apparatus for igniting and monitoring the flames of gas burners such as are used in household and industrial gas appliances, e.g. stoves, hot water and space heaters, clothes dryers, etc. More particularly it relates to an improved ignition and monitoring apparatus that depends for operation on the inter relation of ignition, flame monitoring, and fuel control.

Gas fired burners of the type described have in the past been ignited conventionally by the use of a constantly burning pilot flame. If the pilot flame were extinguished, interlock systems caused the fuel valve to close to thereby protect against the escape of unburned gas from the main burner. One system uses a thermocouple mounted to be heated by the pilot flame. The signal from the thermo couple is connected to energize a valve in the main fuel line. If the pilot flame is absent, there is no thermocouple signal to hold the main fuel line valve open and consequently the total gas supply is shut off.

A major disadvantage of ignition of a gas burner by a pilot flame system of the type described is the ease with which the flame may be extinguished by draft. On automatic appliances such as hot water heaters, furnaces, and overhead radiant heaters, this disadvantage can be costly as well as inconvenient. Most users of such appliances hesitate through fear or lack of knowledge to relight a pilot flame and, instead, call the utility company for service. A service call that requires only that a pilot flame be reli-ghted is obviously wasteful and furthermore the user is without the service of the appliance until the gas flame is relighted. Another disadvantage of the pilot flame is that it is permanently extinguished by a temporary interruption of gas service and thus causes the same problems to the user as when extinguished by a draft.

A still further disadvantage of the conventional pilot flame-thermocouple assembly is that the whole assembly may be accidentally moved away from the immediate vicinity of the main burner by a parts failure or carelessness in servicing. Such movement can result in a high concentration of unburned gas since the valve in the main supply line is allowed to remain open by the pilot-flame energized thermocouple even though the flame itself is not close enough to the gas burner to cause immediate ignition. The longer the delay before ignition occurs under such circumstances, the greater is the chance for a damaging explosion.

Electrical systems for igniting and monitoring gas flames have heretofore been proposed. However, prior systems have generally not provided adequate protection against open or short circuited electrodes or they have been expensive and complex in construction. This latter fact has resulted in electrical ignition circuits being generally unreliable in operation.

Accordingly, a principal object of my invention is to provide improved apparatus for igniting and monitoring the flames of gas burners by an electrical ignition system which is reliable, provides protection against the principal hazards and is simple and economical in construction.

Another object of my invention is to provide apparatus of the type described which causes ignition by an electrical spark rather than by a pilot flame and which further utilizes the same electrodes which provide the spark to monitor the gas flame after ignition.

Still another object of my invention is to provide apparatus of the kind described which permits gas to flow to the gas burner only if current is flowing through the electrodes which provide the ignition spark.

Another object of my invention is to provide apparatus of the kind described which does not permit gas to flow to the gas burner if the electrodes which provide the ignition spark are shorted together.

A further object of my invention is to provide apparatus of the type described in which the valve in the gas line supplying the gas burner is not opened until after a continuing electric spark has been established in the vicinity of the burner, to thereby prevent supplying gas to the burner unless the means of igniting the gas are operable.

Yet another object of my invention is to provide an ignition and monitoring system of the type described which depends on the presence of a main burner flame in the spark gap region for the main gas valve to be held open after ignition, rather than on the assumption that because the pilot flame is burning, the main burner has actually ignited and continues to burn.

A feature of some embodiments of my invention is to provide, in a system of the type described, means for timing the igniting spark so that after a period just long enough to cause ignition under normal conditions, the function of the spark gap is switched to measure the impedance of the gap to determine if a flame has been produced and, if it has been produced, to monitor its presence and to hold the main gas valve open only so long as the flame is present. This feature of the invention makes it impossible for the gas to flow from the main burner for more than this minimal time even if the spark gap assembly has been inadvertently displaced from the combustion region. Hence, the likelihood of a buildup of a dangerous gas concentration is reduced.

Another feature of some embodiments of my invention is the positioning of the ignition and monitoring spark gaps in the flame region of the main burner in such a way that, if the flame is temporarily extinguished by drafts or cfuel interruption, the residual heat from the electrodes of the gap and from the adjacent burner will keep the gap conductive of the monitoring spark for a few seconds and the monitoring spark will be of sufficient intensity to reignite the burner if normal gas flow is restored during this time. This feature of the invention is particularly useful in avoiding unnecessary maintenance when safety regulations require that the burner controls must be recycled manually in the event of automatic shut-down.

Other objects and features of my invention will in part be obvious and will in part appear herein-after.

My invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangements of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will 'be indicated in the claims.

For :a fuller understanding of the nature and objects of my invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a diagram, partly pictorial and partly in block and line form showing the environment of the method and apparatus of my invention;

FIGURE 2 is a schematic circuit diagram illustrating explained below.

toring function after a short interval.

J apparatus made according to and utilizing the method of my invention;

FIGURE 3 is an alternative construction for a portion of the apparatus of FIGURE 2;

FIGURE 4 is a schematic diagram of an alternative construction to that shown in FIGURE 2 which includes means for determining if the spark electrodes of FIGURE 2 are short-circuited together and for interrupting the gas I supply if this in fact occurs; and

FIGURE 5 is a schematic diagram of a simplified apparatus utilizing my invention .for use in environments Where the likelihood of displacement of the electrodes from the vicinity of the gas flame is not a major consideration.

In FIGURE 1, a gas burner 12 of the type conventionally used in gas appliances, is supplied with gas of the type normally used for domestic and industrial heating through a manually operated valve 14, a pressure regulating valve 16, and an automatic control valve 18. The valves are all of conventional design.

An ignition control circuit to be hereinafter described, is connected via leads 22 and 24 to the solenoid 18a of the valve 18. Additionally, two electrodes 26 and 28 are supplied from the control circuit 20. A spark gap 30 is formed between the ends of these two electrodes to ignite the gas from the burner 12. The power supplied to the ignition control circuit 20 via leads 31 and 32 is controlled by a thermostat 34, which monitors the temperature of the medium to which the heat of the burner 12 is supplied and by relay operated by the thermostat '34. Thus, if the burner is used as a space heater, the thermostat 34 may be measuring air temperature. The relay 35 will operate to close the contacts 35a and 35b. Power is then supplied from the power inlet terminals 36 and 38 to the ignition control circuit 20. The specified thermostat arrangement by which this is accomplished is conventional and forms no part of my invention.

The manually operated valve 14 is used for emergency and service shut-downs and in normal operation remains open. The regulating valve 16 is set to reduce the supply pressure to a valve suitable for the type of gas and the design of burner 12.

When heating is required, the thermostat circuit 34 connects power terminals 36 and 38 to the ignition control circuit 20 in the manner described. The circuit 20 energizes the spark gap electrodes 26 and 28 with suflicient energy to cause a spark to pump the gap 30 and ignite gas coming from burner 12. Ignition control circuit 20 is designed to energize and open control valve 13 only if a continuing spark is present at spark gap 30 as will be In one embodiment of the invention, if the electrodes 26 and 28 forming the spark gap 30 have been separated, or short circuited to ground in such a way as to prevent a spark from occurring, ignition control circuit 20 will not energize valve 18 and no gas can flow into the burner 12. If spark gap 30 is correctly adjusted, and a spark does occur, valve 18 is energized, gas flows into burner 12 and is quickly ignited.

In another embodiment of my invention I provide in the ignition control circuit, means for determining if the electrodes are short circuited together. If this condition occurs, either when ignition is attempted or after combustion is in progress, the valve 18 will be de-energized thereby preventing dangerous escape of gas when no spark can occur.

Whether or not a spark occurs at the spark gap 30 or gas ignites at burner 12 in some embodiments of my invention the ignition control circuit 20 is designed to switch the spark gap circuit from a sparking to a moni- An interval of five seconds is typically sufficient to ignite burner 12 if gas is present and if the spark is occurring. When the spark gap 30 is switched to a monitoring function, it measures the impedance in the space between the spark gap electrodes and allows the valve 18 to remain open only if the impedance is characteristic of a flame. If, for example, the thermostat 34 calls -for heat but the valve 14 is closed, no ignition can occur as a consequence of the sparking at gap 30, even though the valve 18 has been opened by the sparking. When monitoring starts, gap 30 still has the high impedance characteristic of normal air and the control circuit 20 will, therefore, cause the valve 18 to close. If, on the other hand, gas is available and the burner 12 ignites, the gap 30 performs its monitoring function. If thereafter the flame is extinguished by a gas supply interruption or a draft, the impedance at gap 30 will rise slowly as the gap electrodes cool and will soon cause valve 18 to close so that if gas flow is restored or the draft ceases, there will be no danger of unignited gas flowing from burner 12. Further, if the electrode impedance drops very sharply as when a short circuit occurs across the gap 30 this condition may also be sensed and the valve 18 closed to prevent continuing gas supply.

If, however, the conditions for normal combustion are restored before the valve 18 closes, the monitoring spark re-ignites the burner automatically and thus makes unnecessary a manual recycling of the control circuit to the ignition function.

One embodiment of a circuit for performing the ignition control function is illustrated in FIGURE 2. As shown therein the ignition control circuit includes a thermal time delay relay generally indicated at 40 which includes a resistive element 42 and a switch having a pair of fixed contacts 44a and 44b and a movable contact 440. As shown the resistive element 42 of the timer 40 is connected across the power supply lines and is energized upon operation of relay 35. After approximately five seconds, during which time the resistive element 42 heats up, the switch contact 440 switches from contact 44b to contact 44c.

The ignition control circuit also includes a transformer 46 having a primary winding 48 and a secondary winding 50. The primary winding 48 is tapped as at 48a and this tap is connected to contact 4412 of the thermally timed switch. One terminal of the primary winding is connected to the power supply terminal 32 and the other end of the winding to the switch terminal 44a.

One end of the secondary winding of transformer 50 is connected to one of the spark gap electrodes, as for example electrode 26 and the other end of the electrode 28 through a full wave bridge rectifier formed by the diodes 52, 54, 56 and 58. A capacitor 60 is connected across the bridge rectifier to by-pass large transient voltage spikes and noise which may be generated by the electrodes during the ignition portion of the cycle. The rectified output voltage of the full wave bridge rectifier is connected to the coil 62a of relay '62. The normally open contacts 62b of the relay 62 when closed supply power to the solenoid 18a of the valve 18 to cause it to open and supply gas to the burner 12.

The operation of the circuit of FIGURE 2 is as fol lows. When line voltage is applied to the leads 31 and 32 it is also applied through the contacts 44c and 44b of the thermal time delay 40 to about one-third of the primary winding 48 of the transformer 46. This produces a high voltage across the secondary winding 50 of the transformer 46, the high voltage being sufiicient to cause a spark between the electrodes. The full-wave rectifier formed by the diodes 52 through 58 rectifies the alternating current drawn by the electrodes and this rectified current operates relay 62 in turn causing operation of the solenoid valve 18. The capacitor 64 is connected in parallel with the relay coil to smooth the pulsating direct current supplied by the rectifier. If, for any reason, there is no electrode current, the gas supply is not turned on. This is an important consideration, since if there is any malfunction of the ignition control circuit which would prevent ignition no unburned and potentially explosive gas can accumulate in the appliance.

After an interval of a few seconds, typically five, during which the existence of a spark is proven and the gas supply is turned on, ignition should have occurred. The time delay relay 40 then switches the line voltage to the full primary winding 48 of transformer 46 by operation of contact 440 to engage contact 44a and thus reduces the voltage on the secondary winding 50 to a value somewhat less than half that necessary to produce an igniting spark. The reduced voltage is sufficient, however, to cause a spark to bridge the gap between the electrodes 26 and 28 in the presence of flame produced ions which ions will be present when flame is present and for a brief period after the flame is extinguished. Therefore an alternating current is maintained through the rectifier sufficient, when rectified, to operate relay 62 and maintain the gas supply open. In the event that the flame is extinguished by a temporary interruption of gas service or by a strong draft, the reduced secondary voltage soon becomes inadequate to bridge the gap 30 between electrodes 26 and 28 and the relay 62 is de-energized thus cutting off the gas supply.

If either of the two electrodes becomes short-circuited to ground during either the ignition or supervisory phase of operation as discussed above, no current will flow in the rectifier circuit and relay 62 will be de-energized thereby shutting off the gas supply. The same would be true for excessive separation of the electrodes or the likely failure of any component in the system.

It should be noted also that in the circuit of FIGURE 2 once the time delay relay 40 has shifted from its initial high voltage position to the low voltage position, it remains in this position until the line voltage is removed for a long enough period to re-cycle the time delay relay.

An alternative embodiment of my invention using a silicon-controlled rectifier (SCR) is shown in FIGURE 3. As there indicated an SCR66 is connected with its anode and cathode in series with one of the power supply leads to the solenoid 18a of the valve =18. A resistor 68 is connected across the leads from the rectifier to replace the coil 62a of relay 62 and provide a path for load current to fl'ow to and from the electrode 28. The positive end of the rectifier signal is connected to the gate of the SCR66 through capacitor 70. The other bridge lead is connected to the cathode of the SCR. The resistor 72, also in series with the solenoid 18a is of such a resistance and wattage rating that it will burn out if the SCR fails to a short circuit condition, thereby permanently de-energizing valve 18. The diode 74 allows the solenoid 18a to be energized for only one polarity of applied voltage, and in effect short circuits the solenoid for the other polarity of applied voltage so that the voltage generated by the collapsing field of the inductance does not damage the SCR66.

The pulsating direct voltage from the rectifier is passed by the capacitor 70 and energizes the SCR gate to cause conduction during each half cycle of the alternating voltage applied to the solenoid 18a. The voltage from the rectifier is therefore necessary to open the gas valve just as in the embodiment of FIGURE 2 and the circuit operates in substantially the same manner.

The principal advantage of the SCR circuit of FIG- URE 3 over the relay circuit of FIGURE 2 is that when the electrodes 26 and 28 are cold, the circuit of FIGURE 3 will permit a flame extinguishment of several seconds with automtic re-ignition and without the nuisance of manual re-cycling even with cold electrodes. An SCR has essentially no differential between pull-in and drop-out; and only a relatively small electrode current is necessary to switch the SCR. After a flame extinguishment, even when the burner is first ignite-d, there are residual ions between the electrodes and even a few residual ions will permit the transformer secondary voltage to cause a spark to jump the gap between the electrodes and provide the current necessary to operate the SCR. Thus after a flame extinguishment when the burner is first ignited, the gas valve will not close immediately, but will remain open for a few seconds, supplying gas. If the monitoring voltage is sufficient to cause a spark to jump the gap, because of the ions present, the gas will reignite. An SCR in place of the relay :62 in FIGURE 2 thus prevents what are called nuisance failures when the burner is first ignited. However, the sensitivity of the SCR that makes this possible may lead to indecisive chattering as the residual ions in the spark gap gradually reduce in number to a point where it will no longer conduct.

The relay, on the other hand, because it requires substantial current to operate it, drops out almost immediately after the flame is removed from the electrodes when the burner is first ignited and cannot overlook nuisance failures. Thus the desirability of using the circuit of FIGURE 2 or the alternative circuit of FIGURE 3 depends on the anticipated rate of nuisance failure and the importance, or non-importance of overlooking them.

In FIGURE 4 I have illustrated another embodiment of my invention which performs the functions of the circuits of FIGURES .2 and 3 and also prevents operation of the gas valve 18 if the electrodes '26 and 28 are shorted together. Additionally, a relay circuit is provided in conjunction with the operation of the thermal time delay relay 40 in the circuit of FIGURE 4 so that the time delay relay need not remain energized during the entire period of combustion. Rather power is removed from the resistive element of the time delay relay when the relay operates as will be explained below.

As shown in FIGURE 4 a relay generally indicated at is provided with a coil 80a and two sets of contacts 8% and 800. One terminal of the coil 80a is connected to the terminal 32 directly and the other is connected to the terminal 31 through the normally open switch elements 44c and 44a of the thermal time delay relay 40. The coil, when energized, is also connected to the terminal 31 through the normally open contacts of the set of relay contacts identified as 8012. The second set of relay contacts 800 operates to switch line voltage from the center tap 48a of the transformer 46 to the entire primary winding when the circuit shifts from the ignition mode to the monitoring mode of operation as described above in connection with FIGURE 2.

The relay 80 operates in conjunction with the timer 40 in the following manner. When power is applied to the terminals 31 and 32 by the operation of the thermostat or other controlling device, relay 80 remains in the position shown in FIGURE 4. Accordingly power is applied through the normally closed contacts of the contact set 800 and resistor 82, whose purpose will be explained below, to the center tap 48a of the primary winding 48 of transformer 46. Power is also applied through the normally closed contacts of contact set 80b to the resistive element 42 of the thermal time delay relay 40. After a period determined by the time require-d to heat the element 42 to its operating temperature, movable contact 440 engages fixed contact 44a in the timer. This causes relay coil 80a to be energized and the relay operates. The operation of relay 80 removes power from the resistive element 42 and connects the upper end of the coil 80a of the relay 80 to the terminal 31 through the normally open (but now closed) contacts of the contact set 80b. Thus, the thermal time delay relay can now recycle to its normal state, without affecting circuit operation. However, relay 80 will remain operated so long as power is applied to the terminals 31 and 32. Additionally, when relay 80 is operated, power is applied through the normally open contacts of the contact set 800 to the entire primary winding of the transformer 48, thus reducing the voltage across the spark gap 30 when flame is present. It will be noted that a resistor 84 is provided in the connection from the contact set 800 to the entire primary winding just as resistor 82 was provided in the connection to the tap of the transformer.

A circuit for sensing whether the electrodes of the spark gap are short circuited together is also provided in FIGURE 4. Its operation is based on the fact that if the electrodes are not shorted, they will present a relatively high impedance which will be reflected to the primary side of the transformer 46. If the reflected impedance is placed in series with a fixed impedance, such as resistors 82 or 84, and the size of these resistors is appropriately selected, then a substantial voltage will appear across the primary winding of the transformer. However, if the electrodes are short-circuited together, a relatively low reflected impedance will appear across the transformer primary and almost all the applied voltage will then appear across one of the series resistors 82 or 84, depending on whether or not relay 80 is operated. The amplitude of the voltage appearing across the primary winding of the transformer 48 is sensed and is used to cause operation of relay, which in turn controls the application of power to solenoid 18a of the gas supply valve 18.

As shown in FIGURE 4, the circuit includes a resistor 86 connected in series with a diode 88 and capacitor 90, this series combination of elements being connected in parallel with the primary winding 48 of the transformer 46. One end of the coil 92a of a relay 92 is connected to the junction of capacitor 90 and diode 88, the other end being connected to one terminal of the Zener diode 94. The other terminal of the Zener diode is connected as shown to the terminal 32. A set of normally open contacts 92b operated by relay 92 is connected in series with the power lead to the coil 18a of the valve 18. Thus, in order for valve 18 to operate to supply fuel to the burner, the relay 92 must be operated.

The resistor 86, diode 88 and capacitor 90 function as a rectifying and filter circuit, rectifying the voltage appearing across the primary winding 48 of the transformer 46 and applying it to the coil 92a of relay 92. The Zener diode 94 in series with the coil of the relay insures that a minimum direct voltage must be present across the ca acitor 90 to prevent the relay 92 dropping out, and thereby shutting off the gas supply.

If the electrodes 26 and 28 are not short-circuited together, adequate voltage will appear across the primary winding to hold relay 92 operated because of the relatively high reflected impedance. However a short circuit, either temporary or permanent, will cause the relay 92 to drop out, thus removing the gas supply from the burner so long as the short circuit continues. While a temporary short circuit will cause interruption of the gas supply, if the short circuit is removed in a relatively short time the burner will re-ignite provided the electrodes have not cooled to the point where an arc can no longer jurnp across them with the monitoring voltage applied to them.

It will also be noted that I provide an additional set of normally open contacts 620 on the relay 62 in the circuit of FIGURE 4. These contacts are connected in series with the lead supplying power to the primary winding 48 of transformer 46 when the circuit is in the monitoring mode of its operation. This additional set of contacts removes power from the primary winding of transformer 46 and from the short circuit detection circuit when, for some reason, relay 62 has dropped out during the monitoring mode of operation. The function of contact set 620 is to remove all power from the ignition transformer if the relay 62 drops out for any reason. In the monitoring mode of operation of the circuit of FIG- URE 4 the relay 62 is effectively held in the operated state by power supplied to it through its own normally open contact. If for any reason of power failures, component failure, or flame extinguishment for any reason the relay 62 drops out, the circuit must then go through the ignition cycle of its operation before power can again be applied to the electrodes 26 and -28.

the burner.

Another embodiment of my invention is illustrated in FIGURE 5. This circuit is similar to the circuits de-' scribed above in connection with FIGURES 2 and 4 but omits the elements of those circuits necessary to cause a reduction in voltage from the ignition mode to the monitoring mode. The construction of the circuit is substantially identical to the circuit shown in FIGURE 4 except for this omission, as will be apparent from an inspection thereof. Accordingly it will not be further described in detail.

When power is applied to the terminals 31 and 32 in FIGURE 5, it is applied directly to the primary of transformer 46 and therefore to electrodes 26 and 28. So long as the electrodes 26 and 28 are not short-circuited together relay 92 will operate as described above. If current is drawn by the electrodes 26 and 28, relay 62 will operate, as described in connection with FIGURE 2 above, solenoid valve 18 will be operated and fuel will be supplied to the burner.

The circuit of FIGURES 2 and 4 provide for proof of flame i.e. during the monitoring mode of operation, the circuit will interrupt the supply of fuel, unless a flame is present at the electrodes. Alternatively, if the fuel supply is interrupted the circuit will shut off the solenoid valve 18. In contrast, the circuit of FIGURE 5 provides for proof of spark only, i.e. it insures that the electrical portions of the circuit are properly operative, but does not check for the presence of flame. The circuit of FIGURE 5 would be particularly useful for controlling ignition where the presence of flame is otherwise monitored, either by an operator or by other known electrical or temperature sensing means. The particular advantage of the circuit of FIGURE 5 is its simplicity and therefore relatively low cost as compared to the circuits of FIG- URES 2 and 4.

It will be noted that one end of the secondary winding 50 of the transformer 46 in the circuits illustrated in FIGURES 2, 3, 4 and 5 is grounded and that the other end of the transformer, the high voltage end, is connected to the electrode 26. The measurement of current is made between the low voltage electrode 28 and' ground. Thus, it there is a breakdown in the insulation surrounding the lead carrying the high voltage to the electrode 26, so that current flows to the surrounding housing, Which is usually at ground potential, current flow through the rectifier circuit is interrupted and the valve 18 will close, preventing the escape of unburned gas.

The circuit arrangement described is an improvement over prior electrical ignition control circuits which sometimes monitored the current drawn by the electrodes by current sensitive devices connected either in series with the primary winding of the transformer, or by devices connected in series between the lower end of the secondary winding and ground. Prior circuits of this type could not distinguish between current flowing in the secondary winding of the transformer due to sparking across the spark gap and that resulting from the shorting of the high voltage electrode to ground. Accordingly, use of prior circuits of the type described was dangerous since unburned gases might accumulate around the ignition electrodes with their attendant explosive hazard.

It will thus be seen that I have provided improved apparatus for the control of ignition of a hydrocarbon fuel burner. In some embodiments of my invention I provide a single set of electrodes which both ignite the gas and monitor it, the electrodes being supplied with appropriate voltages in timed sequence to perform both of these functions. Failure of the electrodes to spark in the ignition phase results in the main gas valve not opening. In some embodiments of my invention, I also provide means for sensing if the electrodes are short circuited together and 1f so I provide means for interrupting the fuel supply to In those embodiments where the flame is monitored, the absence of flame in the monitoring phase causes the fuel supply to be interrupted. The apparatus of my invention also shuts off the gas for any flame-outs but if the flame-out is of short duration, the gas burner of my invention will relight automatically. I have also located the apparatus for monitoring the current at the ignition electrodes in such a way that current must be flowing through the electrodes and not just in the secondary of the transformer for ignition to occur. Apparatus made according to my invention is obviously simple and reliable in operation and economical of construction.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are etficiently attained and, since certain changes may be made in the constructions set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

I claim:

1. An ignition control system for a hydrocarbon fuel burner comprising in combination:

(1) a set of electrodes in close proximity to said burner, said electrodes defining a spark gap therebetween, said gap being positioned to ignite fuel emitted from said burner;

(2) an electrically-controlled valve in the fuel supply line to said burner, said valve supplying fuel to said burner when in the operated condition;

(3) a transformer having primary and secondary windings;

(4) means connecting the secondary winding of said transformer to said electrodes;

(5) means including a series impedance connecting the primary winding of said transformer to a source of alternating electrical power;

('6) and means responsive to the voltage appearing across said primary winding for preventing operation of said valve so long as the voltage across said winding is below a predetermined level.

2. The combination defined in claim 1 which includes means for sensing current through said electrodes, and means for operating said valve only if current is flowing through said electrodes.

3. The combination defined in claim 1 in which said means responsive to the voltage across the primary winding of said transformer includes a relay and means associated with said relay for establishing a reference voltage level, such that if the voltage applied to said relay falls below a predetermined value, said relay will be deenergized, thereby preventing operation of said fuel supply valve.

4. An ignition control system for a hydrocarbon fuel burner comprising in combination:

(1) a set of electrodes in close proximity to said burner, said electrodes defining a spark gap therebetween, said gap being positioned to ignite fuel emitted from said burner;

(2) an electrically controlled valve in the fuel supply line to said burner;

(3) means for supplying a voltage sufficient to cause sparking across said spark gap during a first predetermined interval;

(4) current responsive apparatus connected in series with said electrodes to cause operation of said valve if current is flowing through said electrodes as a result of application of said sparking voltage;

(5) means for supplying a lower voltage to said electrodes after said first predetermined time, said lower voltage being insuflicient to cause a spark across said spark gap in air, but sufficient to cause current to flow through said electrodes if said electrodes are immersed in a flame;

(6) said valve operating means maintaining said valve in operated condition so long as current flows through said electrodes when said lower voltage is applied thereto.

5. The combination defined in claim 4 which includes means for preventing operation of said valve when said electrodes are short circuited together.

6. An ignition control system for a hydrocarbon fuel burner comprising in combination:

(1) a set of electrodes in close proximity to said burner, said electrodes defining a spark gap therebetween, said gap being positioned to ignite fuel emitted from said burner;

(2) an electrically controlled valve in the fuel supply line to said burner;

(3) a transformer having primary and secondary windmgs;

(4) means connecting the secondary winding of said transformer to said electrodes;

(5) means including a series impedance connecting the primary of said transformer to a source of alternating electrical power;

(6) said connecting means including means for supplying a voltage sufficient to cause sparking across said spark gap during a first predetermined time interval, and for supplying a lower voltage to said electrodes after said predetermined time interval, said lower voltage being insufficient to cause a spark across said gap in air, but sufficient to cause current flow through said electrodes if said electrodes are immersed in a flame;

(7) means for operating and maintaining said valve in operated condition if current is flowing through said electrodes during either of said intervals; and

(8) means responsive to the voltage appearing across the primary winding of said transformer for preventing operation of said valve unless said voltage is above a predetermined level.

7. An ignition control system for a hydrocarbon fuel burner comprising in combination:

(1) a set of electrodes in close proximity to said burner, said electrodes defining a spark gap therebetween, said gap being positioned to ignite fuel emitted from said burner;

(2) an electrically controlled valve in the fuel supply line to said burner, fuel being supplied to said burner when said valve is in the operated condition;

(3) a pair of power input terminals for connection to a source of alternating voltage;

(4) a time delay relay including a resistive element and a switch, said switch being operated from a first to a second condition a predetermined time following energization of said resistive element;

(5) means connecting said resistive element to said power input terminals;

(6) a transformer having a primary and secondary winding, the primary winding having fewer turns than said secondary winding and said primary winding being tapped;

(7) means connecting one end of said primary winding to a first of said power input terminals;

(8) means connecting said primary winding tap and the other end of said primary winding through a switch controlled by said time delay relay to the second of said power input terminals, whereby said tap is connected to said second power input terminal when power is first applied to said power input terminal, and after said predetermined time, the other end of said primary winding is connected to said second power input terminal;

(9) means connecting the ends of said secondary winding to said electrodes, said connecting means including means for developing a control signal in response to the current flowing through said electrode;

(10) and means responsive to said control signal for causing said electrically controlled gas supply valve to be operated to thereby supply fuel to said burner.

8. The combination defined in claim 7 in which said means responsive to said control signal includes an electromagnetic relay.

9. The combination defined in claim 7 in which said means responsive to said control signal includes a silicon controlled rectifier.

10. The combination defined in claim 7 which includes means for preventing operation of said valve when said electrodes are short circuited together.

11. The combination defined in claim 7 which includes means responsive to the voltage appearing across said primary winding for preventing operation of said valve so long as the voltage across said winding is below a predetermined level.

12. An ignition control system for a hydrocarbon fuel burner comprising in combination:

(1) a set of electrodes in close proximity to said burner, said electrodes defining -a spark gap therebetween, said gap being positioned to ignite fuel emitted from said burner;

(2) an electrically controlled valve in the fuel supply line to said burner, said valve being opened when in operated condition;

(3) a transformer having a primary and a secondary winding;

(4) means connecting the primary winding of said transformer to a source of alternating electric power;

(5) means connecting one end of said secondary winding of said transformer to one of said electrodes;

(6) means connecting the other end of said transformer secondary winding to ground;

(7) means connecting the other of said electrodes to ground, said connecting means including current responsive apparatus, said apparatus for genera-ting a control signal when current flows therethrough; and

(8) means responsive to the presence of said control signal for causing operation of said electrically controlled valve.

13. The combination defined in claim 12 in which said current responsive means includes a diode bridge having opposite diagonal corners connected respectively to said electrode and to ground, said control signal appearing across the other pair of opposite diagonal corners of said bridge and in which said means responsive to said control signal includes an electromagnetic relay.

14. The combination defined in claim 12 in which said current responsive means includes a diode bridge having opposite diagonal corners connected respectively to said electrode and to ground, said control signal appearing across the other pair of opposite diagonal corners of said bridge and in which said means responsive to said control signal includes a silicon controlled rectifier.

15. An ignition control system for a hydrocarbon fuel burner comprising in combination:

(1) a set of electrodes in close proximity to said burner, said electrodes defining a spark gap therebetween, said gap being positioned to ignite fuel emitted from said burner;

(2) an electrically controlled valve in the fuel supply line to said burner, said valve being opened when in operated condition;

(3) a pair of power input terminals for connection to a source of alternating voltage;

(4) a time delay relay including a resistive element and a switch, said switch being operated from a first to a second position a predetermined time following energization of said resistive element;

(5) means connecting said resistive element to said power input terminals:

(6) a transformer having a primary and secondary winding, the primary winding having fewer turns than said secondary winding and said primary winding being tapped;

"(7) means connecting one end of said primary winding to a first of said power input terminals;

(8) means connecting said primary winding tap and the other end of said primary winding through a switch controlled by said time delay relay to a second of said power input terminals, whereby said tap is connected to said second power input terminal when power is (first applied to said power input terminal, and after said predetermined time, the other end of said primary winding is connected to said second power input terminal;

(9) means connecting the ends of said secondary winding to said electrodes, said connecting means including a diode bridge rectifier, a first terminal of said bridge rectifier being connected to one end of said secondary winding and a second terminal of said bridge rectifier diagonally opposite to said first terminal being connected to one of said electrodes and (10) means responsive to the signal appearing between the diagonally opposite third and fourth terminals of said bridge circuit to cause operation of said electrically controlled valve.

16. The combination defined in claim 15 which includes means connecting the end of said secondary winding of said transformer which is connected to said rectify ing means to ground.

17. The combination defined in claim 15 in which said means responsive to the signal appearing between the third and fourth terminals of said bridge includes an electromagnetic relay whose contacts, when said relay is operated, cause power to be supplied to said electrically controlled valve.

18. The combination defined in claim 15 in which said means responsive to the signal appearing between the third and fourth terminals of said bridge includes a silicon controlled rectifier having an anode, a cathode and a gate terminal, said anode and cathode being connected in series with the power supply line to said electrically controlled valve, said signal being supplied to the gate and cathode terminals of said silicon controlled rectifier.

19. An ignition control system for a hydrocarbon fuel burner comprising in combination:

(1) a set of electrodes in close proximity to said burner, said electrodes defining a spark gap therebetween, said gap being positioned to ignite fuel emitted from said burner;

(2) an electrically controlled valve in the fuel supply line to said burner;

(3) a transformer having primary and secondary windings;

(4) means connecting the secondary winding of said transformer to said electrodes;

(5) means including a series impedance connecting the primary winding of said transformer to a source of alternating electrical power;

(6) means for operating and maintaining said valve in operated condition if current is flowing through said electrodes; and

(7) means responsive to the voltage appearing across the primary winding of said transformer for preventing operation of said valve unless said voltage is above a predetermined level.

20. The combination defined in claim 19 in which said means for operating and maintaining said valve in operated condition includes a diode bridge rectifier circuit, a first terminal of said bridge rectifier being connected to one end of said secondary winding of said transformer and a second terminal of said bridge rectifier diagonally opposite to said first terminal being connected to one of said electrodes and means responsive to the signal appearing between the diagonally opposite third and fourth terminals of said bridge circuit to cause operation of said electrically controlled valve, said means maintaining said valve in operated condtion so long as current flows through said electrodes.

21. The combination defined in claim 19 in which said means responsive to the voltage appearing across the primary winding of said transformer includes an electromechanical relay and means associated with said relay for establishing a reference voltage level, such that if the voltage applied to said relay falls below a predetermined value, said relay will be de-energized thereby preventing continued operation of said valve.

22. A method of igniting and monitoring the flame of a hydrocarbon fuel burner supplied with fuel through a fuel control valve comprising, in combination, the steps of (1) supplying a high voltage to a pair of electrodes defining a spark gap in the vicinity of said burner;

(2) measuring the current drawn by said electrodes and opening said control valve if said current is above a predetermined level;

(3) reducing the magnitude of the voltage supplied to said electrodes after a predetermined time;

(4) continuously measuring the current drawn by said electrodes with said reduced voltage applied thereto;

(5) and closing said control valve when the current through said electrodes drops below a predetermined value.

23. The method defined in claim 22 in which said reduced voltage is not more than one-half the high voltage applied to said electrodes.

24. The method defined in claim 22 which includes the step of monitoring said spark gap to determine the presence of a short circuit across it and shutting off said fuel supply if a short circuit appears.

References Cited by the Examiner UNITED STATES PATENTS 4/ 1930 Fischer et a1.

4/ 1941 Clark.

4/ 1941 Fanger.

2,948,335 8/1960 Hegwein 158-28 X FREDERICK KETTERER, Primary Examiner. 

12. AN IGNITION CONTROL SYSTEM FOR A HYDROCARBON FUEL BURNER COMPRISING IN COMBINATION: (1) A SET OF ELECTRODES IN CLOSE PROXIMITY TO SAID BURNER, SAID ELECTRODES DEFINING A SPARK GAP THEREBETWEEN, SAID GAP BEING POSITIONED TO IGNITE FUEL EMITTED FROM SAID BURNER; (2) AN ELECTRICALLY CONTROLLED VALVE IN THE FUEL SUPPLY LINE TO SAID BURNER, SAID VALVE BEING OPENED WHEN IN OPERATED CONDITION; (3) A TRANSFORMER HAVING A PRIMARY AND A SECONDARY WINDING; (4) MEANS CONNECTING THE PRIMARY WINDING OF SAID TRANSFORMER TO A SOURCE OF ALTERNATING ELECTRIC POWER; (5) MEANS CONNECTING ONE END OF SAID SECONDARY WINDING OF SAID TRANSFORMER TO ONE OF SAID ELECTRODES; (6) MEANS CONNECTING THE OTHER END OF SAID TRANSFORMER SECONDARY WINDING TO GROUND; (7) MEANS CONNECTING THE OTHER OF SAID ELECTRODES TO GROUND, SAID CONNECTING MEANS INCLUDING CURRENT 